Effective treatment for substance use disorders is a national priority. Therapeutic communities (TCs), an important treatment modality, provide a highly structured social learning environment to encourage positive changes in behavior, attitudes, and self-image. Successful outcomes for TC treatment are correlated with time in treatment; yet, attrition from TCs is disturbingly high. We believe that stress mediates progress and retention in TCs and that stress reduction strategies are needed to assist clients to manage the inherently stressful environment of the TC. A number of studies document the promise of Mindfulness-Based Stress Reduction (MBSR) in reducing stress in a variety of clinical and non-clinical populations. We have preliminary data to demonstrate that MBSR decreases stress in TC clients as evidenced by a decrease in awakening salivary cortisol measurements. This study is designed to translate our MBSR findings into behavioral treatment for TCs to enhance engagement and retention of clients. The proposed Stage 1 Behavioral Development research will refine and test the first MBSR program based on a manual, as an adjunct to TC treatment. The study will: 1) operationally define and standardize principles and techniques of MBSR; 2) pilot test and refine MBSR in TC treatment; and 3) test hypotheses evaluating the potential of MBSR to influence stress, which is proposed as the mediator of progress and retention. Stress will be measured with salivary cortisol and the Perceived Stress Scale. Progress is conceptualized as progression toward re-entry to society, global self-change and internalized self-change. These outcomes will be measured with a facility point system, standard TC measures and linguistic analysis of stress descriptions, respectively. Retention will be measured with facility admission and dropout records. Data will be analyzed using general linear mixed models to address change over time and a standard analysis approach for examining mediation effects.